The present invention relates to an eddy-current meter of the type having a permanent magnet rotated by a shaft whose speed is to be measured, a metal cup close to the permanent magnet and attached to a spindle carrying a pointer. The spindle is rotatable against the bias of a spiral spring, the pointer being associated with a calibrated scale or dial. The eddy-current meter is usable as a tachometer or speedmeter.
In an eddy-current meter of the above type, as the permanent magnet revolves, eddy currents are produced in the metal cup. The magnetic fields caused by these eddy currents produce a torque, which acts in a direction to resist the turning magnetic field. The metal cup will turn against the spiral spring, in the direction of the rotating-magnetic field, and will turn (or be dragged) until the torque developed by the eddy currents equals that of the spiral spring.
A conventional eddy-current meter of the above type has a spindle carrying a pointer mounted with an axial end play. This end play is apt to cause variation of the distance between the metal cup and the permanent magnet hence there is variation of the torque applied to the metal cup when the meter is installed in a vehicle that takes varying positions from the vertical. Thus correct indication by the pointer is hardly possible when the meter is installed in such vehicle. To eliminate the axial end play, it has been proposed to arrange a plate spring over a dial to exert an axial force on the spindle. However, the arrangement detracts from the appearance of the dial, and means for adjusting the axial force makes construction of the meter complicated.